Web guiding method and apparatus



June 25, 1963 J. D. ROBERTSON ETAL 3,

WEB GUIDING METHOD AND APPARATUS Filed July 6, 1959 7 Sheets-Sheet 1 INVENTORS JOHN D. ROBERTSON BYRAYMOND H. FOSTER KENWAY, JEWELWYEERIQHifDR'zIT-T ATTORNEYS June 25, 1963 J. o. ROBERTSON ETAL 3,095,131

WEB GUIDING METHOD AND APPARATUS Filed July 6, 1959 7 Sheets-Sheet 2 FIG?) INVENTORS JOHN D. ROBERTSON BYRAYMOND H. FOSTER KENWAY, .IENN EY WlTl'ER & HILDRETH ATTORNEYS June 25, 1963 J. n. ROBERTSON ETAL 3,095,131

WEB GUIDING METHOD AND APPARATUS Filed July 6, 1959 7 Sheets-Sheet 3 lllllli llllll INVENTORS JOH D. ROBERTSON BYRAY ND H; FOSTER WY, JEHNEY, WITIER & HILDRETH FIG.6

ATTORNEYS June 25, 1963 J. o. ROBERTSON ETAL 3,095,131

WEB GUIDING METHOD AND APPARATUS Filed July 6, 1959 7 Sheets-Sheet 4 INVENTORS JOHN D. ROBERTSON BY RAYMONDIH. FOSTER KENWAY, 15mm, wins; a. HILQRETH ATTORNEYS June 25, 1963 .1. n. ROBERTSON ETAL 3,095,131

WEB GUIDING METHOD AND APPARATUS Filed July 6, 1959 v 7 Sheets-Sheet 5 FIG.II

F|G.l2

FIG.

INVENTORS JOHN D. ROBERTSON BY RAYMOND H. FOSTER NEWAY .lENHEL WITI'ER & HILDRETH ATTORNEYS June 25, 1963 .1. D. ROBERTSCN ET-AL 3,095, 31

WEB GUIDING METHOD AND APPARATUS Filed July 6, 1959 '7 Sheets-Sheet 6 55 F IG. l6

INVENTORS JOHN D. ROBERTSON BYRAYMOND H. FOSTER MEIMAY JENBH. WKUER & HILDRFJH ATTORNEYS June 25, 1963 J. D. ROBERTSON ETAL 3, 9

WEB GUIDING METHOD AND APPARATUS '7 Sheets-Sheet '7 Filed July 6, 1959 INVENTORS ROBERTSON JOHN D. RAYMOND H. FOSTER KLNNAY, JENNEY, WITTER & HILDRETH ATTORNEYS 3,095,131 WEB GUlDING METHOD AND APPARATUS John Douglas Robertson, Tauntou, and Raymond H. Foster, Norton, Mesa, assignors, by mesne assignments, to Mount Hope Machinery Company, Taunton, Mass-,

a corporation of Massachusetts Fiied July 6, 1959, Ser. No. 825,074 10 Claims. (Qt. 226190) This invention relates to a novel method and apparatus for guiding and aligning traveling webs of various materials such as paper, fabrics, etc. of varying gauge and flexibility, and especially to novel method and apparatus for correcting misalignment of the web without causing wrinkling or otherwise damaging the web.

In accordance with a preferred embodiment of our invention we feed the traveling web forwardly-rearwardly and rearwardly-forwardly about two web supporting abutments and correct any misalignment in the web by pivoting the abutments laterally as a unit in one direction or the other whereupon the web is biased in the correcting direction. We have discovered that when the web as thus biased is led through equal helical paths about the abutments the web maintains its straight alignment about the abutments and no wrinkling of the web results. It is also desirable that the web shall contact the abutments with minimum possible friction, especially for fragile webs, and our invention contemplates improvements whereby such minimum friction is effected through the employment of rotary abutments and the web made to pass through said helical paths and correct misalignment without wrinkling or damaging the web, all as hereinafter more specifically described.

An important feature of the invention relates to the employment of a rotary abutment in the form of a cylindrical roller having a plurality of web supporting bars extending longitudinally thereon at its periphery and disposed in parallel relation concentrically about the rotary axis of the roller, the bars being movable both forwardly and laterally with the web and thereby conducting the web freely in a helical path on and about the roller without placing appreciable tension on the web. The production of a novel method and apparatus for thus facilitating the web guiding and aligning functions comprises a further object of the invention.

These and other features of the invention will be best understood and appreciated from the following description of preferred embodiments thereof selected for purposes of illustration and shown in the accompanying drawings in which:

FIG. 1 is a fragmentary perspective view of a Web guiding device embodying our invention,

FIG. 2 is a plan view thereof,

FIG. 3 is a fragmentary side elevation,

PIG. 4 is an end elevation, partially broken away, of a segmented web guiding roller shown in FIGS. 1-3,

FIG. 5 is a side elevation of the roller, partially broken away,

FIG. 6 is a fragmentary elevation, partially in section, of a modification thereof,

FIG. 7 is an end elevation of a further modification thereof,

FIG. 8 is an enlarged elevation of a portion of the roller shown in FIG. 7,

FIG. 9 is a view like FIG. 3 but showing a modification thereof,

FIG. 10 is a like view showing a further modification,

FIG. 11 is a fragmentary plan view of a modified construction including certain automatic controlling mechanism,

FIG. 12 is a like view of the parts in a different position,

3,@5,l3i Patented June 25, 1963 FIG. 13 is a fragmentary view thereof in end elevation,

FIG. 14 is an enlarged fragmentary top plan view of FIGS. 11 and 12 with the parts in another position,

FIG. 15 is a front elevation of FIG. 14,

FIG. 16 is a bottom plan view of the FIGS. 14 and 15,

FIG. 17 is an enlarged fragmentary detail view taken on line 1717 of FIG. 15, and

FIG. 18 is a plan view partly in section of a segmented roller utilized to change the direction of travel of a web.

Referring first to the form of invention illustrated in FIGS. 1-5, it) indicates the supporting base of our web guiding device which is adapted to be fixed to and supported on the machine employed for feeding the traveling web 12. The machine is adapted to feed the web forwardly in the direction indicated by the arrows and the function served by our invention is automatically to maintain the web in true feeding alignment and including the automatic correction of any misalignment that may develop as the web travels forwardly, as to a rewinding roll 14. Two parallel web guiding rolls 15 and 17 are rotatably supported on the base 10 and our web guiding mechanism is disposed between these rolls to receive the web from the roll 15 and deliver it to the roll 17.

Our Web guiding mechanism as illustrated in FIGS. 1-5 employs two parallel web supporting abut-ments 18 and 26, both comprising rollers rotatably mounted at their ends in the upright portions 21 of a frame including a tubular bar 22 rigidly supporting the two uprights at its two ends. The frame is mounted for pivotal movement on a post 24 extending through the bar and supported in a yoke 25 carried on the base lit. The rolls 15 and 17 are disposed right-angularly across the web 12 and in the normal position of the frame 2122 the abutments 13 and 2% are parallel with the rolls 15 and 17. The pivoting of the frame is under the control of automatic sensing mechanism herein indicated as a sensing finger at 26 in contact with one edge of the web 12 and frame pivoting mechanism including a cylinder 27 having a piston therein provided with a piston rod 28 connected to the bar 22. The arrangement is such that under normal conditions and when there is no misalignment in the web the frame 2122 will remain in its normal position. However, should the web deviate laterally in one direction or the other the finger 26 Will follow the web and cause pivoting of the frame in a direction to correct the misalignment. Such sensing mechanisms are known in the art, as for example, in Patents 2,291,830 and 2,814,- 487, and per se form no part of this invention.

The web 12 is fed forwardly in a plane path P (FIG. 3) onto and arcuately about the roller 18, from thence rearwardly to and arcuately about the roller 20, and from thence forwardly in a second plane path P parallel with the path P. The sensing finger 26 is disposed to contact the edge A of the web forwardly of the roller 20. If, for example, the entering portion of the web at P shifts gradually to the left (FIG. 2) a distance Y from its normal position, the finger 26 will sense the change and cause pivoting of the frame 21-22 to an angular position to correct the misa ignment. It should be understood however that this lateral shifting of the web is immediately sensed by the finger 26 which, operating through the cylinder 27, functions immediately to correct the misalignment and such functioning continues so long as there is any continued increase in the amount of misalignment. As illustrated, this angular displacement of the rollers 18 and 26 causes the web to move to the right. During such movement the web remains in contact with the finger 26 thereupon causes the frame 21-22 to remain in such position as will continue to correct the misalignment.

Men the web 12 passes around the rollers 18 and 20,

as illustrated in FIG. 2, it would follow equal helical paths therearound if no friction were present where it contacts the rollers. However, since each part of the roller in contact with the web moves in a circular path about the axis of the roller and whereas the helically moving web also travels longitudinally of the roller there is necessarily a frictional sliding relation between the web and roller. We have found that whereas the tensioned web vwill pass in a true helical path around one rotary roller it tends to wrinkle and tear when passing therefrom to and in reverse relation about the second rotary roller. This action is due to the frictional contact of the web with the rollers and the fact that the web necessarily travels laterally whereas each roller point of contact travels in a plane circular path. Our invention contemplates novel means for eliminating this difficulty and substantially eliminating the frictional relation between the web and at least one roller. We accomplish this object by making one or both of the abutments 18 and 20 a segmental roller in which the web engaging and supporting portions not only rotate with the roller but also travel longitudinally therealong with the lateral movement of the web. This mechanism as illustrated in FIGS. lwill now be described.

In FIGS. 1-5, we have illustrated the abutment 18 as embodying a plain cylindrical roller and the abutment 2b as embodying a segmented roller. The segmented roller includes two flanges 30 fixed in spaced relation on an axle 32 mounted to rotate in bearings 33. Supported for free longitudinal movement in aligned bushings 34 in the flanges are a plurality of bars disposed concentrically about the axle, each bar embodying a web supporting shoe 36 having end portions 37 welded thereto and slidable longitudinally in the bushings 34. The shoes illustrated are of T-shape and are supported for rotation with the axle by rollers 38 riding in longitudinal channels 40 in a hub 42 secured to the axle as by a set screw 43. As best illustrated in FIG. 4, the shoes provide contiguous Web supporting surfaces entirely around the peripheral portion of the roller.

As illustrated in FIG. 4 the forwardly moving web contacts the roller at its lowermost portion, passes 180 therearound in contact with the shoes 36 and leaves at its topmost portion, and the bars 3637 are free to travel longitudinally with and thus accommodate lateral movement of the web during this passage. Also cooperating with the end portions 37 at the two ends of the roller are two cam tracks 44 disposed to contact the free ends of portions 37 during their idle travel'downwardly (FIG. 4) and thus centralize the shoes 36 longitudinally as they reach the web-engaging position.

In some cases it may be desirable to avoid frictional sliding contact of the bar end portions 37 with the cam contacts 44 and in FIG. 6 we have illustrated a modified construction for this purpose. In this case the two cam tracks 44 have been replaced by two disks 46 each mounted at the angle illustrated in FIG. 6 on a hub 48 carried on the axle 32. Each disk is mounted to rotate on ball-bearings 50 and is rotated with the roller by means of a pin 52 carried by the roller and extending through a hole in the disk. As will be apparent, the lowermost portions of the two disks are spaced apart a distance to engage the ends of the bars 36--37 and centralize them as they approach the web-engaging position. It may also be desirable to face the disks with rubber or other shock absorbing material illustrated at '54.

I Other means can be provided for centralizing the Web supporting bars 36-37 and in FIGS. 7 and 8 we have illustrated a modified construction for this purpose.

portions 56 projecting from one end thereof and outwardly beyond the adjacent supporting flange 30 and each such portion carries a laminated soft iron core 58 therein. A solenoid coil 68 surrounding each such portion and core is grounded to the flange 3.0 and .to a con- In. this case the web supporting bars have non-magnetic end tact 62 carried by the bar and spring pressed into engagement with a commutator strip 64. The web enters and leaves the roller as indicated by the arrows in FIG. 7 and during the downward idle movement of the bars the contacts serve to energize the coils whereupon the cores are centralized therein and serve to centralize the Web supporting bars.

It will now be apparent that the segmental bars 36-37 provide web supporting means on the roller 20 that travel both forwardly and laterally with the web, thereby accommodating the lateral shifting of the web during its helical passage about the roller and eliminating the webroller friction heretofore present. Thus the freely movable bars in effect provide a frictionless roller 20 whereby the Web delivered thereonto from its helical path about the roller 18 freely follows a true helical path about the roller 20, thereby eliminating any canting and wrinkling of the web as occurs when both rollers present frictional resistance to the lateral movement of the web.

We are aware that non-rotary abutments 18 and 20 can-be employed at 18 and 20 without causing wrinkling of the web between the abutments but the friction required to be overcome with such abutments, both longitudinally and laterally of the web, is very objectionable and troublesome, especially with light and fragile webs which cannot sustain the work load thus placed on the web. The use of rotary abutments which eliminates the longitudinal friction is highly desirable and our invention herein makes such use possible with two companion rollers and. furthermore eliminates the lateral friction in at least one of the abutments. As illustrated in FIGS. 3 and 9, either abutment 18' or 20 can employ the segmental roller embodied in our invention and except for the added expense involved, the use of our segmental roller for both abutments, as illustrated in FIG. 10, eliminates longitudinal and lateral friction in both abutments and provides substantially perfect helical frictionless tracking of the web about the abutments. 'In FIG. 9 the segmental roller is shown at 65 and the plain roller at 66 and in FIG. 10 two segmental rollers 67 are employed.

While in the form of invention shown in FIGS. 11() We have mounted the web supporting bars 36-37 for free longitudinal movement on the roller 20 and have depended on the web for moving the bars longitudinally in the helical tracking of the web, our invention alsocontemplates a positive moving of the bars to accommodate the lateral shifting of the web and to guide it through the required helical path about the roller. The machine shown in FIGS. 11-17 of the drawings for performing this function will now be described.

The web supporting abutments 68 and 70 shown in FIGS. ll'17 correspond to the abutments 18 and 20 shownin FIGS. 1-10 and comprise rollers rotatably mounted in a like frame including plates 72 rigidly supported on the ends of a bar 74 pivoted at 75 on an upright 76 rigidly supported on a plate 77 corresponding to the base 10. The web supporting bars 78 are herein illustrated as cylindrical rods having reduced end portions 79 mounted to slide longitudinally through bushings in spaced'flanges 80 carried on an axle 82 mounted in hearing supports 84. The web 12 is fed forwardly in a plane path P (FIG. 13) to and arcuately about the plain roller abutment 68, thence rearwardly to and arcuately about the segmented roller abutment 70 and thence forwardly in a plane path P parallel with the path P.

Whereas in the invention illustrated in FIGS. l-lO the web functions to move. the bars 3637 longitudinally therewith as the web travels helically about the roller 20, the mechanism shown in FIGS. 11'17 provides means for automatically moving the bars 78 longitudinally to con-' form to the lateral shifting movement of the web as the web travels in a helical path about the roller. The mechanism for performing this function includes two flexible cam tracks in contact with the ends of the websupporting bars together with a novel system of levers for automatically flexing the cam tracks into helical form of varying degree pitch when flexed from the normal position by pivotal movement of the abutment supporting frame 72-74.

The two cam tracks comprise two flexible annuli 85 respectively in contact with the ends of the bars 78-79 at the two ends of the roller. Each such annulus is anchored at its bottom portion to a bracket 86 extending inwardly from the adjacent bearing support 84. Diametrically opposite thereto each annulus is split and its two ends hinged together on a pivot pin 88. The ends of each such pin are supported in a yoke 89 on one end of a link 90 pivotally connected at 91 at its other end to a lever 92 pivoted at 93 to a bracket on the adjacent plate 72. The other ends of the two levers 92 at the ends of the roller are pivotally connected at 94 to two links 95 in turn pivoted together on a fixed post at 96.

When the frame 7274 is in the position shown in FIG. 11 the two cam tracks 85 are in two parallel planes and hold the web supporting bars 7879 centralized therebetween, each annulus 85 being anchored in such plane on its bracket 86. In such position each cam face is right angular to the rotary axis of the roller and each pin 88 is parallel to the face of its cam. The distance C between the pivots 91 and 93 (-FIG. 14) is equal to 1rD/ 2 D being the diameter of the segmental roller. The distance between pins 94 and 96 is equal to the distance between the pivots 75 and 93 and the distance between pivots 96 and 75 is equal to the distance between pivots 94 and 93, thereby forming a parallelogram with corners at 75, 93, 94 and 96. When the frame 72-74 is pivoted about the axis 75 in either direction from the neutral position shown in FIG. 11, to correct misalignment of the web, one lever 92 pivots outwardly and the other inwardly and flexes the cam tracks equally and in opposite directions into helical configuration. This configuration in each track forms a cam face helix extending from the fixed portion thereof at 86 to the hinged pivot 88 and from thence back to the anchor 86 and the pitch of the helix varies with the pivoted extent of the frame.

It will now be apparent that the web supporting bars 78 and 79 are held in fixed centralized position when the frame 72T4 is in the neutral position of FIG. 11 and that as the frame is pivoted about the pin 75 in either direction from the normal the two cam tracks 35 are flexed to helical shape adapted to move the bars longitudinally upon rotation of the roller and carry all web engaging points thereon through the true helical path required. This bar-moving helical path corresponds with the forward movement of the web through 180 on the roller from the point 97 to the point 98 (FIG. 13) and during the remaining 180 rotation of the roller the other half of the cam tracks return the bars to centralized position. It is noted that the 180 wrap of the web on the roller from point 97 to point 98 is a distance 1rD/2 which is equal to the distance between the pivot 93 and the axis of the roller. While we have herein illustrated the web as wrapped 180 about the rollers it should be understood that other degrees of wrap may be employed so long as the entering and exiting reaches P and P of the web are maintained parallel.

Also while we have herein specifically illustrated and described our novel segmented rollers 20 and 70 as employed in combination with certain web guiding and aligning mechanism, we desire it to be understood that such rollers are adapted to serve other useful and important web guiding functions within the scope of our invention. For example, it may be desired to change the direction of travel of a web (as shown in FIG. 18) or to reverse the two faces of a web and our novel rollers are adapted to perform these and other like functions with facility and without causing wrinkling or otherwise disturbing the free and uninterrupted travel of the web.

We are aware that many modifications may be made tudinal travel of the web which it provides.

by those skilled in the art without deviating from our invention.

An important advantage of this guiding mechanism is the high ratio of lateral guiding displacement to longi- The high ratio is made possible because of the fact that during operation of the device, both edges of the web follow paths of equal length during corrective lateral displacement.

This is accomplished by causing both edges of the web to travel in helical paths about cylindrical abutments. When the web is pulled around a cylindrical abutment, the path tends to be helical since the shortest distance between two points on a cylinder is a helix. When the web edges travel in such helical paths, the web has a lateral component of motion. Obviously the lateral motion is required to provide the necessary lateral guiding correction. When the web is traveling about a fixed abutment, there is a force opposing its motion over the abutment equal to the amount of friction between the web and the abutment. The source of available force is the tension applied to the web by power driven take-up rolls, or the like, located beyond the guiding mechanism. This force overcoming the friction lies on the surface of the abutment and is parallel to the lengthwise direction of the web. Therefore, the direction of slippage of the web on the surface of the abutment is in the direction of the pull of the web; i.e., parallel to the center line of the web.

When no guiding correction is required, the axis of the abutment is oriented normal to the desired path of the web and there is no lateral component of motion of the web in passing around the abutment. When a guiding correction is required, the axis of the abutment is tilted about an axis perpendicular to the approaching web and the tension of the outgoing web pulls the oncoming web about the abutment in the shortest path, which is a helix, because friction force opposing the motion of the web acts parallel to and in the opposite direction to the relative motion of the web and the surface of the abutment.

When the abutment is a non-rotatable cylinder, the path of the web is a helix. When the abutment is a plain rotatable cylinder, the pull of the outgoing web rotates the cylinder instead of sliding the web over it, thus tend ing to guide each lengthwise element of the in-coming web away from its desired path, and into a plane at right angles to the axis of the rotating cylinder and passing through the last previous point, which controlled the location of the element. Usually such last previous point is the location of the element as it leaves the roll immediately before the rotating abutment mentioned above.

If a freely rotatable slatted cylindrical abutment is used with linear anti-friction bearings between the slats and their supports, the friction between the web and the slats is sufllcient to move the slats in the direction and to the amount required to permit the web to be pulled in a helical path.

Having thus disclosed our invention what we claim as new and desire to secure by Letters Patent is:

l. A web guiding apparatus comprising in combination, means including two parallel web supporting abutments for guiding a traveling web forwardly through a predetermined plane path to and arcuately about one of said abutments, from thence rearwardly to and arcuately about the other abutment and from thence forwardly in a plane path parallel with the first named path, one of said abutments being a cylindrical roller and including a plurality of web engaging bars extending longitudinally thereof and disposed in parallel relation concentrically about the rotary axis of the roller, means supporting the bars for longitudinal movement on the roller, means cooperating with the ends of the bars for automatically centralizing them longitudinally uuon rotation of the roller to a predetermined position, a frame supporting said abutments at their ends and including means rotatably supporting the roller, and means supporting the frame for pivotal movement about an axis disposed normally to'the planes of said paths.

2. The combination defined in claim 1 in which the bars are supported for free movement longitudinally and said means cooperating with the bars comprises cam tracks disposed automatically to centralize the bars longitudinally upon rotation of the roller by contact of the ends of the bars with said tracks, and means for rotating the cam tracks with and at the ends of the roller.

3. The combination defined in claim 1 in which the bars are supported for free movement longitudinally and said means cooperating with the bars comprises a plurality of solenoids respectively cooperating with the bars and having contacts disposed to engage a commutator track located at one end of the roller.

7 4. The combination defined in claim 1, in which said means cooperating with the ends ofv the bars comprises two resilient cam tracks respectively located at and contacting the two ends of the bars, and means for automatically flexing the cam track into helical form of varying degree pitch as the frame is rotated in one direction or the other about said axis from a neutral position in which said abutments extend right-angularly across said paths.

5. The combination defined in claim 4 in which each of said cam tracks comprises a resilient annulus anchored at one peripheral portion thereof to said frame and having its diametrically opposite portion split into two ends and hinged together on a radial axis, and in which the last named means comprises a system of levers connected to the hinged portions of the tracks.

6. The combination defined in claim 5 in which said system of levers comprises two arms respectively pivoted at one end each to the frame at opposite ends of the roller and connected intermediately of the ends thereof to said hinged portions :of the tracks, and two arms connected together at their inner ends on a fixed pivot and pivoted at their outer ends to the other ends of th first named arms.

7. A web guiding apparatus comprising in combination, means including two parallel web supporting abutments for guiding a traveling web to and arcuate about one'of said abutments and from thence to and arcuately about the other abutment, one of said abutments being a cylindrical roller and including a plurality of web engaging bars extending longitudinally thereof and disposed in parallel relation concentrically about the rotary axis of the roller, means supporting the bars for longitudinal movement on the roller, cam track means cooperating with the ends of the bars for automatically centralizing them longitudinally upon rotation of the roll: er to a predetermined position, a frame supporting said abutments at their ends and including means rotatably supporting the roller, and means supporting the firame for pivotal movement about an axis disposed normally a to the planes of said paths.

8. The combination defined in claim 7 plus means supporting the scam tracks in fixed position relative to the bars and roller.

9. A Web guiding device, comprising a cylindrical roller having a plurality of web supporting bars extend ing longitudinally thereon at its periphery and disposed in parallel relation concentrically aboutthe rotary axis of the roller, means mounting the roller for rotation on said axis, means supporting the bars for free. longitudinal movement on the roller parallel with said axis,

' which each flexible annulus normally rests in a common plane disposed right angularly to said axis, and means disposing the annuli into helical form of varying degre pitch when flexed from the normal position.

References Cited in the file of this patent UNITED STATES PATENTS 678,121 Lewis ..L July 9, 1901 1,493,954 Bolton May 13,4924 1,833,289 Hiller Nov. 24, 1931 2,287,768 Eckstein June 30, 1942 2,301,545 Hlavaty Nov. 10, 1942 2,532,562 Lorig Dec. 5, 1950 2,558,761 Kentis July 3} 1951f 2,576,233 Lorig Nov. 27, 1951 2,643,146 Hasselquist June 23, 1953' 2,731,262 Morrow Tan. 17, 1956 2,752,151 Levine June 26,1956 2,821,387 Faeber Jan. 28, 1958 FOREIGN PATENTS 765,976 France Apr. 9, 1934 474,415 Canada June 12, 1951 

1. A WEB GUIDING APPARATUS COMPRISING IN COMBINATION, MEANS INCLUDING TWO PARALLEL WEB SUPPORTING ABUTMENTS FOR GUIDING A TRAVELING WEB FORWARDLY THROUGH A PREDETERMINED PLANE PATH TO AND ARCUATELY ABOUT ONE OF SAID ABUTMENTS, FROM THENCE REARWARDLY TO AND ARCUATELY ABOUT THE OTHER ABUTMENT AND FROM THENCE FORWARDLY IN A PLANE PATH PARALLEL WITH THE FIRST NAMED PATH, ONE OF SAID ABUTMENTS BEING A CYLINDRICAL ROLLER AND INCLUDING A PLURALITY OF WEB ENGAGING BARS EXTENDING LONGITUDINALLY THEREOF AND DISPOSED IN PARALLEL RELATION CONCENTRICALLY ABOUT THE ROTARY AXIS OF THE ROLLER, MEANS SUPPORTING THE BARS FOR LONGITUDINAL MOVEMENT ON THE ROLLER, MEANS COOPERATING WITH THE ENDS OF THE BARS FOR AUTOMATICALLY CENTRALIZING THEM LONGITUDINALLY UUON ROTATION OF THE ROLLER TO A PREDETERMINED POSITION, A FRAME SUPPORTING SAID ABUTMENTS AT THEIR ENDS AND INCLUDING MEANS ROTATABLY SUPPORTING THE ROLLER, AND MEANS SUPPORTING THE FRAME FOR PIVOTAL MOVEMENT ABOUT AN AXIS DISPOSED NORMALLY TO THE PLANES OF SAID PATHS. 